In recent years, in the fields, such as vehicles, security robots, unmanned helicopters, and the like, requests to perform obstacle detection in a proceeding direction accurately for the purpose of collision prevention, have been increasing. As methods of detecting obstacles, a laser radar which is a distance measuring apparatus utilizing optical scanning, has been known. General laser radars are configured to rotate or oscillate a polygon mirror or the like while projecting light fluxes emitted from a laser light source onto a mirror, the polygon mirror, or the like so as to scan a wide range and to receive scattered light rays from a projected object with a light receiving element, thereby performing distance measurement.
PTL 1 discloses a technique with regard to a polygon mirror which includes the even number of planar reflective surfaces and performs scanning by reflecting light rays the even number of times.